You philological linguophiles and your derivates! :elfroleeyes: And yet we still don't have "rolleyes" spelled correctly. :tongueelf: I can see it going either way, Amarie, though I am inclined to believe it's a combination, that Morgoth placed Maiar spirits in twisted corruptions he made of Erus creations. In the original, LT2 version, of Beren and Luthien in prose, Huan speaks as a matter of routine, while in the Silm he speaks but thrice in his long life, yet we have the captain of the werewolves make a dying declaraton to Sauron after his battle with Huan. And it's well established Morgoth nor Melkor was capable of creation, only the perversion of existing creations; add the fact Dragons are clearly living creatures and they can only be either corrupted but preexisting life and/or Maiar in physical form.
Setting aside epistemology and inspiration (according to lore the "snakes" St. Patrick drove from Ireland were the Druids, who used the serpent as a symbol of wisdom, as does scripture on at least two occasions) I don't think Morgoth had it in him to give a dumb beast speech and human (at least) intelligence, but I also don't think it would be possible for any mortal to kill Glaurung or any other Dragon in any permanent sense if they were purely Maiar. So the most reasonable conclusion seems, to me, that the Dragons, Werewolves and likely many other horrible things besides known only to the Professor, were combinations of existing animal life and Maiar. That makes it a lot easier to explain Smaug and Scatha lasting from the First Age; while they COULD be offspring, reproducing Dragons have no precedent in canon, or even in apocrypha so far as I know. If you have an immortal beast due to a Maiar spirits presence reproduction becomes far less necessary, and we don't have to explain the apparently inherent evil of a Dragon brood.
As to the specific issue of Earendils combat with Ancalagon, the Silmarillion says only this (following a passage with the appearance of the previously unknown winged Dragons "so sudden and ruinous... that the host of the Valar was driven back:")
But Earendil came, shining with white flame, and about Vingilot were gathered all the great birds of heaven and Thorondor was their captain, and there was battle in the air all the day and through a dark night of doubt. Before the rising of the sun Earendil slew Ancalagon the Black, the mightiest of the dragon-host, and cast him from the sky; and he fell upon the towers of Thangorodrim, and they were broken in his ruin.
(Of the Voyage of Earendil, p.252 in the 1977 George, Allen and Unwin hardback)
This is the only canonical mention of the battle, or of Ancalagon at all (stuff like this is what drew me to HoMe.) It does tell us much, but much of that presents as many questions as answers. First, we see a combat between two armies, which Ancalagon and Earendil appear to lead (though it DOES say Thorondor was the captain of the Eagles, or perhaps of "the great birds" in general, though I know of no others in canon.) Even that assumes the Dragons were led by the greatest of their members, and not by Sauron or the mind of Morgoth himself, but this seems reasonable given the cunning and intellect we see in Glaurung and Smaug.
It's impossible to tell if Earendils combat with Ancalagon was "Roman style" or an aspect of the larger fray, but if the former it begs the question of what kept Vingilot aloft not merely in the heavens but over Thangorodrim. In this he is not simply put through the Doors of Night as part of the celestial realm, but in Middle-earth, and flying. Not only that, but his ship is with him, which to me suggests something like the swans of Alqualonde drawing the ships of Teleri.
Beyond that we can say little save the HOSTS fought the rest of the day and the entire night, and Earendil personally slew Ancalagon ere dawn. Ancalagons fall broke "the towers of Thangorodrim;" is this the mountain itself, or merely its battlements, which latter the Wreck of Gluarung, or even Smaug would likely have done? We don't know. Ancalagon is called "the mightiest of the dragon-host" but this seems to mean "the host of Dragons in the fight" from which Glaurung is obviously excluded since he's dead.
Hence my conundrum; Ancalagon is unquestionably the greatest of the flying dragons, but could something of Glaurungs bulk fly? If the winged dragons were so fiercesome, why were they not used 'til the War of the Powers? The most logical answer to the latter is that air superiority was of little value in the previous wars (though you'd think it would come up in the Fall of Gondolin) as to the former, I can't decide, though I lean toward "Ancalagon was the greatest of the Dragons, bar none."